Systems and methods for temperature control and heat extraction from waste landfills

ABSTRACT

The field of the invention relates to systems and methods for exchanging heat from the degradation, decomposition, and chemical/biochemical transformation of municipal, industrial, and other types of waste. In one embodiment, a heat extraction system may include a closed-loop fluid circulation piping channeled throughout at least one heat extraction well oriented throughout a waste mass. The piping is fluidly coupled to a heat exchanger. A first circulation fluid is circulated through the closed-loop circulation piping into various depths of the waste mass to transfer thermal energy between said mass and said heat exchanger. In one embodiment, the transfer of thermal energy between the waste mass and the heat exchanger is used as alternative energy method and to control at least one of shear strength, compressibility, and hydraulic conductivity of the waste mass.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority to U.S. patent application Ser.No. 13/190,313 filed Jul. 25, 2011, which is hereby incorporated byreference in its entirety.

FIELD OF THE INVENTION

The field of the invention relates to systems and methods fortemperature control and heat extraction, and more particularly tosystems and methods for controlling and manipulating temperature andextracting heat from the degradation, decomposition, andchemical/biochemical transformation of municipal, industrial, and othertypes of waste.

BACKGROUND OF THE INVENTION

Continued increases in generation of industrial and municipal solidwaste (MSW) has resulted in increased use of landfill sites worldwide.The U.S. Environmental Protection Agency estimates that the MSWgeneration in the U.S. is approximately 240 million tons (U.S. E.P.A.2009). A significant portion of the waste is disposed of in landfills.As MSW landfills undergo normal operation, the primary byproducts of thelandfill processes are heat, gas, and leachate (i.e., contaminatedliquid generated due to passage of liquid through the waste mass).Significant amounts of other types of wastes such as industrial waste,agricultural waste, mining waste, and other types of wastes also aregenerated in the U.S. on an annual basis.

Turning to FIG. 1, an example of a typical waste landfill 100 isillustrated. Generally, a low permeability barrier 103 is placed overground surface 105. The waste mass 101 is deposited and landfilled uponthe barrier 103. Waste mass 101 may consist of, for example, alternatinglayers of soil and trash. The landfilled waste mass 101 is covered witha low permeability cover 102. The total depth 104 of waste landfill 100varies, for example, between tens to hundreds of feet.

In the waste that is buried or landfilled, the organic componentsdecompose resulting in generation of heat and gas that can be convertedto usable energy. A considerable amount of energy is produced in thismanner. In fact, a mid-sized landfill—such as the Riverview Landfill inRiverview, Mich.—can provide energy equivalent to 10,000 residentialhomes. A number of recognized techniques for effectively using landfillsites are based on, for example, collecting the gas produced fromdecomposed waste and converting to energy or maintaining conditions forrecycling leachate. Furthermore, these techniques attempt to minimizeboth nearby contamination and atmospheric pollution.

For example, waste decomposition in a landfill produces an effluent gas,which contains about fifty percent (50%) methane (CH₄). This landfillgas in the interior of the landfill is often at a higher pressure thanthat of the surrounding atmosphere. Consequently, this pressuredifferential creates a migration pattern of the landfill gas towardsboth the surface (vertically) and near the edges/perimeter(horizontally) of the landfill. However, methane is an inflammable gasthat not only can damage plants in a nearby area but also lead to adanger of explosion. Additionally, emission into the atmosphere of thelandfill gas contributes to the “greenhouse effect” as a direct factorto abnormal climate phenomena. With respect to environmental pollution,where the level of methane contained in the landfill gas is in theamount of 50 to 60%, the influence on the “greenhouse effect” isapproximately 21 times or greater compared to that of carbon dioxide(CO₂). However, as methane also has a beneficial combustion property, itis possible to collect the gas from a landfill to provide an efficientenergy resource.

A conventional technique of controlling the withdrawal of gas from alandfill site is to drill deep vertical wells, such as well 106 in FIG.1, into the landfill. These vertical wells are attached to a network ofpipes and gas pumps (not shown) to vacuum/extract gas from the wells. Anexample of such a system implementing this technique is disclosed inU.S. Pat. No. 7,448,828, to Augenstein et al., filed Feb. 23, 2007 for a“Landfill design and method for improved landfill gas capture,” which ishereby incorporated by reference in its entirety. This systemcontemplates an improved method for collecting landfill gas byminimizing the collection of atmospheric air with the gas.

Another example of effective landfill use controls gas generation ratesof the landfill through leachate regulation. This technique involvesregulating both temperature and pH levels of leachate to be recycled andcontinuously injected into a deposit of wastes. For example, see U.S.Pat. No. 6,334,737, to Lee, filed Dec. 17, 1999 for a “Method andapparatus of controlling landfill gas generation within a landfill,”which is hereby incorporated by reference in its entirety. Monitoringand controlling a variety of conditions for recycling leachate providesthe advantage of maintaining, as consistently as possible, the level ofgas production during the landfill process.

Significant amount of research and development has been reported for gasand leachate. However, less information is available on heat generationin landfills. Elevated temperatures can affect the ongoing biochemicalprocesses (e.g., decomposition) and mechanical and hydraulicproperties/behavior of the wastes. Operational and climatic conditionshave significant effects on heat generation and transfer in landfills.For example, see Yesiller et al., for “Heat Generation in MunicipalSolid Waste Landfills” (Yesiller, N., Hanson, J. L., and Liu, W.-L.,Journal of Geotechnical and Geoenvironmental Engineering, ASCE, Vol.131, No. 11, p. 1330-44 (2005)) and Yesiller and Hanson, for “Analysisof Temperatures at a Municipal Solid Waste Landfill” (Yesiller, N. andHanson, J. L. “Analysis of Temperatures at a Municipal Waste Landfill,”Sardinia 2003, Ninth International Waste Management and LandfillSymposium, Christensen et al. Eds., CISA, Italy, p. 1-10 (2003)), whichare hereby incorporated by reference in their entirety. These effectsmay be short-term (e.g., reaction rates) and/or long-term (e.g.,microbial population balance within the waste). In general, wastedecomposition rates generally increase with increased temperatures up toa point of killing microbial populations (e.g., approximately 70° C.).

Temperatures within landfills undergo seasonal fluctuations near thesurface and edges/perimeter of the landfill due, in part, to conductiveand convective heat transfer. Elevated temperatures are correspondinglyobserved within the landfilled mass at central locations. Accordingly,optimal decomposition and gas production conditions are not uniformwithin a landfill mass.

Current systems for energy extraction from MSW landfills focus on thegeneration and distribution of gas and leachate in landfills. However,such systems do not take advantage of a detailed analysis of spatialheat distribution or a long-term thermal trend of landfills. Inaddition, systems are not available for controlling and manipulatingtemperatures in landfills. Furthermore, current systems do not provide amethod for creating a symbiotic energy source between the landfill andnearby facilities to create optimal operating conditions.

Accordingly, a system and method for controlling and manipulatingtemperatures and extracting heat from a landfill that considers heatgeneration and temperature distribution within a landfill is desired.

SUMMARY OF THE INVENTION

The field of the invention relates to systems and methods for heatextraction, and more particularly to systems and methods for controllingand manipulating temperature and extracting heat from the degradation,decomposition, and chemical/biochemical transformation of municipal,industrial, and other types of waste. In one embodiment, a temperaturecontrol and heat extraction system may include at least one heatextraction well providing a channel for a closed-loop fluid circulationpiping that contains a first circulation fluid. The at least oneclosed-loop well extends throughout a waste mass. The closed-loop fluidcirculation piping runs throughout the network of heat extraction wellsand is fluidly coupled to a heat exchanger. The heat exchanger has afirst inlet and outlet for the first circulation fluid and exchangesheat to a second circulation fluid through a second inlet and outlet.The system further includes a highly conductive granular backfillintermittently dispersed within the at least one fluid circulation wellto provide a thermal encasing for said piping. The first circulationfluid is circulated, via a circulation pump operatively coupled to thepiping, through the closed-loop circulation piping into various depthsof the waste mass to transfer thermal energy from said mass to the heatexchanger.

In one embodiment, the waste mass has a first, second, third, and fourthlife cycle stage of biochemical reactions. The transfer of thermalenergy includes the steps of providing a first level of heat to the heatexchanger at the first life cycle stage of a waste mass, wherein theheat exchanger provides heat to said mass through the at least oneclosed-loop fluid circulation well; extracting heat from the at leastone closed-loop fluid circulation well through the heat exchanger at thesecond life cycle stage of the waste mass; providing a second level ofheat to the heat exchanger at the third life cycle stage of the wastemass; and maintaining a long-term heat exchange to or from the wastemass through the heat exchanger at the fourth life cycle stage of thewaste mass.

Other systems, methods, features and advantages of the invention will beor will become apparent to one with skill in the art upon examination ofthe following figures and detailed description. It is intended that allsuch additional systems, methods, features and advantages be includedwithin this description, be within the scope of the invention, and beprotected by the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to better appreciate how the above-recited and other advantagesand objects of the inventions are obtained, a more particulardescription of the embodiments briefly described above will be renderedby reference to specific embodiments thereof, which are illustrated inthe accompanying drawings. It should be noted that the components in thefigures are not necessarily to scale, emphasis instead being placed uponillustrating the principles of the invention. Moreover, in the figures,like reference numerals designate corresponding parts throughout thedifferent views. However, like parts do not always have like referencenumerals. Moreover, all illustrations are intended to convey concepts,where relative sizes, shapes and other detailed attributes may beillustrated schematically rather than literally or precisely.

FIG. 1 is a diagram of a municipal waste landfill known in the art.

FIG. 2 a is a chart representing measurements of temperatures at variousdepths within waste mass as a function of time;

FIG. 2 b is a curve representing general earth temperature trends as afunction of depth.

FIG. 3 is a chart illustrating measured temperatures and analyticallycalculated temperatures within waste mass as a function of time.

FIG. 4 a is a chart representing a series of measured heat contentwithin waste mass for various sites as a function of depth;

FIG. 4 b is another chart representing a series of measured heat contentwithin waste mass for various sites as a function of normalized depth;

FIG. 4 c is a curve representing heat content as a function of initialtemperature of a waste mass.

FIG. 5 is a diagram representing the trend of heat content for varioussites as a function of waste age.

FIG. 6 is a diagram of a heat extraction system in accordance with apreferred embodiment of the present invention.

FIG. 7 a is another diagram of a heat extraction system in accordancewith a preferred embodiment of the present invention;

FIG. 7 b is another diagram of a heat extraction system in accordancewith a preferred embodiment of the present invention; and

FIG. 8 is a chart illustrating exemplary thermal exchange stages inaccordance with a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As described above, heat is generated as a result of biochemicalprocesses and decomposition of organic components in wastes as well aschemical/biochemical transformation of various components in wastes.Field measurements of temperatures within landfills reveal spatialvariations of temperature as a function of depth.

FIG. 2 a illustrates an example of temporal variations in temperaturewith location at a given depth of waste landfill 100. Temperatures atrelatively shallow depths of waste mass 101 (e.g., at the surface aswell as near the edges/perimeter of the waste mass) undergo seasonalfluctuation similar to variability in earth temperature, which is shownin FIG. 2 b. Turning to FIG. 2 b, ground surface 203 provides range T oftemperatures from low temperatures 201 (e.g., 0° C.) to elevatedtemperatures 202 (e.g., 40° C.). Elevated temperatures approachtemperature 204, which is the mean annual earth temperature, as themeasurement depth increases. Range T of temperatures at ground surface203 illustrates a similar trend in waste mass temperatures at shallowdepths in FIG. 2 a.

Conversely, stable, elevated temperatures (e.g., 50-60° C.) can be seennear mid-depth of landfill 100 in FIG. 2 a (e.g., 13-9 meters). Theseasonal variations of temperature within waste mass 101 decreasesignificantly at locations away from the edges of the landfill (e.g., 20meters from air surface). These steady elevated temperatures also mayincrease over time.

At intermediate depths between the edges and center of waste mass 101,temperatures demonstrate phase lag as well as amplitude decrement inrelation to ground-surface temperatures shown in FIG. 2 b. Phase lag canrepresent the delay in timing of peak seasonal temperatures at a givendepth relative to corresponding peaks at the ground surface. Amplitudecan represent the one-half the maximum range of temperature measured ina single year.

Given a typical thermal gradient of waste mass 101 in FIG. 2 a, heatgain in the waste compared to unheated (i.e., ambient) baselineconditions can be determined. This difference between measured wastetemperature, as shown in FIG. 2 a, and unheated baseline wastetemperature at equivalent depths is known as the Heat Content (HC) ofthe waste mass. Specifically, HC represents the average temperaturedifferential of the waste mass as compared to unheated conditions. Inorder to determine the HC, the baseline waste temperatures can bedetermined using equation (1), which is an analytical formulation forground temperature at any depth on any calendar day.

$\begin{matrix}{T_{({x,t})} = {T_{m} - {A_{s}{\mathbb{e}}^{{- x}\sqrt{\frac{\prod}{365\alpha}}}\cos\left\lfloor {\frac{{2\prod}\;}{365}\left( {t - t_{0} - {\frac{x}{2}\sqrt{\frac{365}{\prod\;\alpha}}}} \right)} \right\rfloor}}} & (1)\end{matrix}$where:

T_((x,t))=temperature (° C.) at depth, x and at time, t

T_(m)=mean annual earth temperature (° C.)

A_(s)=amplitude of surface temperature wave (° C.)

x=depth below surface (m)

α=thermal diffusivity (m²/day)

t=time of year, days (where 0=midnight December 31)

t₀=phase constant (34.6 days)

Analytical and numerical approaches have been developed for modelingtemperatures in municipal solid waste landfills with heat generation inwastes due to decomposition, underlying native soil conditions, andoverlying seasonal air temperature fluctuations. A typical example ofthermal modeling for various landfill sites is contained in a study fromHanson et al for an “Analytical and Numerical Methodology for ModelingTemperatures in Landfills” (Hanson, J. L., Liu, W. -L, and Yesiller, N.,Proceedings of Selected Sessions of GeoCongress 08: Geotechnics of WasteManagement and Remediation, ASCE GSP No. 177, Khire et al., eds., ASCE,Reston, Va., p. 24-31 (2008)), which is hereby incorporated by referencein its entirety. In determining a baseline ground temperature profile ina landfill application, thermal diffusivity (α) values betweenapproximately 3×10⁻⁷ m²/sec to 7×10⁻⁷ m²/sec can be used for anequivalent waste mass that is not undergoing seasonal temperaturevariations and not gaining heat due to biochemical decomposition.

With reference to FIG. 3, the HC of a landfill site can be determined bycalculating the area between the time-temperature curves of the measuredwaste temperatures and the analytical baseline unheated wastetemperatures governed by equation (1). FIG. 3 illustrates a typicaltemperature change within waste over time. Temperature curve 302represents a measured temperature within waste mass 101, using sensorarrays or other suitable measurement tools, at a given depth. Forexample, Type K thermocouples deployed in custom-fabricated flexiblesensor arrays ranging from a length between 1 and 60 m for verticalinstallations and between 150 and 200 m for horizontal installations maybe used. These sensors provide high resistance to chemical environmentsand are well suited for landfill applications. Additional informationregarding sensor arrays can be found in an article for “Spatial andTemporal Temperature Distributions in Municipal Solid Waste Landfills”(Hanson, J. L., Yesiller, N., and Oettle, N., Journal of EnvironmentalEngineering ASCE, Vol. 136, No. 8, p. 804-814 (2010)), which is herebyincorporated by reference.

Temperature curve 303 provides equivalent ambient waste temperatures atthe specified depth, calculated using the analytical solution (1)discussed above. As can be seen in FIG. 3, shaded area 304 representsthe area between temperature curves 302 and 303, which provides thetotal heat gain due to biological and chemical activity of waste mass101 in units of degree-days. Furthermore, shaded area 304 can be dividedby the duration of the analysis period to normalize HC with respect totime. The resulting calculation provides HC as a time weighted averageof the change in temperature from unheated conditions in units ofdegrees-centigrade day per day (° C. day/day). Accordingly, thiscalculation provides heat gain in waste mass 101 due to, for example,decomposition, rather than the effects of seasonal/climatic variation oftemperature occurring at the given depth.

The analysis of HC for various locations reveals that higher HC can befound in the central core of waste mass rather than near the edges, topsurfaces, and bases of waste mass 101, as illustrated in FIG. 4 a. FIG.4 a provides typical examples of the variation of HC as a function ofthe depth of the sensors in the waste mass 101. The curves in FIG. 4 ademonstrate elevated heat content near central depths of waste mass. Ineach of these measurements of HC, the HC is linearly related to theinitial waste temperature and waste placement rate (m/year). FIG. 4 cshows the general relationship between measured HC values as a functionof the initial waste temperature.

FIG. 4 b represents the measurements of HC as a function of therespective normalized depth—the ratio of the depth of the measurementover the total depth to linear 104. The curves of FIG. 4 b verify thatthe peak HC occurs at normalized depths near the mass-center (i.e.,normalized depth near 0.5).

Using common exponential growth and decay functions, it is then possibleto model the relationship between HC and the life cycle of a landfill(i.e., time representing the age of waste). Specifically, equation (2)was developed in the form of the Streeter-Phelps approach (presented inVesilind, P. A., 1997, Introduction to Environmental Engineering) formodeling HC as a function of time for waste.

$\begin{matrix}{{HC} = {\frac{a\;\psi}{\left( {b - a} \right)}\left( {{\mathbb{e}}^{- {at}_{w}} - {\mathbb{e}}^{- {bt}_{w}}} \right)}} & (2)\end{matrix}$where:

HC=heat content (° C.-day/day)

a=heat generation constant (day⁻¹)

b=heat utilization constant (day⁻¹)

ψ=heat production potential (° C.-day/day)

t_(w)=waste age (year)

Examples of the model curve generated by equation (2) for sites measuredin FIG. 4 a are illustrated in FIG. 5. FIG. 5 shows the variation of themaximum HC with waste age for various sensors. In general, HC can beseen to increase in a first life cycle of waste degradation (e.g., 2 to4 years for a landfill in a humid continental temperate climate)followed by a period of decrease at a slower rate to a stable low valueof HC.

HC also may be used to determine heat generation of the waste mass. Heatgeneration is defined as the energy required to raise the temperature ofthe waste mass and can be determined using the heat capacity of thewaste, the magnitude of temperature increase of the waste, theevaporation of water into the landfill gas phase, the temperature of thebiochemical reactions, and the heat loss to the surrounding environment.This energy production can be calculated using equation (3).

$\begin{matrix}{E = {\sum\limits_{i = 1}^{n}\;{\Delta\; T_{i}{{cM}(T)}_{i}}}} & (3)\end{matrix}$where:

E=energy production (heat generation, MJ/m³)

ΔT_(i)=increment of temperature rise for waste (K)

c=heat capacity of waste (MJ/m³K)

M(T)_(i)=fraction of energy released that is used for heating a landfill

In order to determine heat generation for various representations of HC,for example, those curves represented in FIG. 4, the peak HC for a givenlocation can be used as the magnitude of temperature increase of thewaste. In this example, with references to FIG. 4 and equation (3), theenergy produced E for HC measurements in FIG. 4 range from 23 and 77MJ/m³ for the various sites. Similar to the results illustrated in FIG.5, variations in energy produced E occurs as a function of waste age.Additionally, energy E peaks and heat content HC peaks are also similarin timing.

Despite low permeability cover 102 used in most landfill sites and therelatively high insulating quality of MSW, heat loss to the surroundingenvironment should be considered in a determination of heat generation.For example, from a central core of waste mass (i.e., the location ofthe highest HC) to an average annual air temperature location (e.g.,landfill cover 102) and subgrade 10 m below the barrier at mean annualearth temperature, the magnitude of conductive thermal losses to thesurrounding environment can range between 42 and 139 MJ/m³-year forlosses towards the cover and atmosphere (upward losses) and between 6and 152 MJ/m³-year for losses towards the barrier and subgrade (downwardlosses). Similarly, convective losses, for example, through leachaterecords, may range between 0 and 11 MJ/m³-year.

As discussed above, biochemical processes of waste decomposition variesas a function of temperature. Current systems attempt to extract energyfrom landfills through the control of the gas production in landfillsites. Temperature conditions may affect the rate at which these systemsproduce usable gas; however, as decomposition produces heat, alternativeuses for the heat energy are typically not utilized.

One approach that benefits from the elevated temperature conditionsdiscussed above is shown in FIG. 6, which shows system 600 for heatextraction in accordance with an embodiment of the present invention.The system 600 preferably includes at least one heat extraction well 601extending throughout waste mass 606. Heat extraction well 601 provides achannel for closed-loop fluid circulation piping 603, which is routedbelow ground surface 602 through heat extraction well 601. In oneembodiment of the present invention, the portion of piping 603 submergedbelow ground surface 602 may be of cross-linked polyethylene (PEX), highdensity polyethylene, copper, or other metal, plastic, or compositematerials. Such piping provides durability in a chemically aggressiveenvironment, resistance to heat, and flexibility for both differentialmovements within waste mass 606 and seismic deformations in waste mass606. However, it is also appreciated by one of ordinary skill that thepiping 603 may also be of any material suitable for heat extraction.

Additionally, the annular space surrounding piping 603 within heatextraction well 601 may be filled with a highly conductive granularbackfill 604 (e.g., dense gravel, soil, or industrial byproduct such asfoundry sand, cement kiln dust, recycled concrete aggregate, etc.) toprovide a material with high thermal conductivity for efficient heattransfer between the fluid circulated in said piping 603 (not shown) andwaste mass 606. An insulating seal 607 is applied at the surface 602 ofwell 601 to prevent convective thermal losses. The piping 603 extendsbeyond ground surface 602 and is fluidly coupled to circulation pump 608and heat exchanger 605. In one embodiment, the portion of piping 603above ground surface 602 may be metal to provide UV resistance.Circulation pump 608 provides fluid flow through the system 600 suchthat circulated fluid through piping 603 conductively transports heatfrom within waste mass 606 to heat exchanger 605.

At ground surface 602, heat can be provided to heat exchanger 605 as analternative source of energy. In one embodiment of the presentinvention, a typical heat exchanger 605 may be a plate and frame heatexchanger that includes a plurality of heat transfer surfaces (notshown) for exposing the heated processed fluid to a second fluid(circulating outside waste mass 606). The heat exchanger 605 furtherincludes a housing having a process fluid inlet and a process fluidoutlet for piping 603.

In operation, the piping 603 conductively transports heat in aclosed-loop system. Processing fluid (not shown) passes through piping603 downwardly into waste mass 606 to conductively transfer elevatedheat upwardly from central depths to the ground surface 602. It is alsoappreciated by one of ordinary skill that the process fluid could alsoflow laterally or at an angle, depending on the orientation of heatextraction well 601 and heat exchanger 605.

A closed-loop system provides heat while reducing public and regulatoryconcern. The fluid used for circulation in piping 603 as well as otherfluids used in the system are self-contained and avoid exposure tocontaminants throughout the process. In one embodiment of the presentinvention, the circulation fluid may be water, which provides a highheat capacity for efficient thermal exchange, propylene glycol, whichprevents the fluid from freezing near surface temperatures in colderatmospheric climates, or a water-glycol mixture. For systems using wateras a circulation fluid, thermostat-controlled trace heaters (not shown)may be used to avoid freezing of the fluid in system components locatedabove a frost line.

A microprocessor computer 609 coupled to both the heat exchanger 605 andcirculation pump 608 may be used to monitor and control pumping ratesand thermal energy transfer in the system. The computer 609 can receiveand manipulate signals including, for example, temperature, position,flow-rate, and time related to the circulated fluid and waste mass via anetwork of sensors (not shown) integrated into piping 603 and throughoutwaste mass 606 electronically coupled to computer 609. Conventionalsensors with means for measuring temperature, position, time andflow-rate can be used to provide computer 609 with control signalsrelating to the circulated fluid and waste mass 606. For example, asdiscussed above, Type K thermocouples deployed in custom-fabricatedflexible sensor arrays may be installed and coupled to computer 609.

The present invention provides an alternative heat source that may beused, for example, by a nearby industry, landfill office, maintenancegarage, scale house, or other industrial, commercial, or residentialfacility. In an alternative embodiment of the present invention, FIG. 7a illustrates system 700 that provides another application for heatextraction. Similar to heat extraction well 601 of system 600, system700 uses a network of heat extraction wells 701 each providing a channelfor a closed-loop circular piping system oriented throughout waste mass706. In one embodiment, heat extraction wells 701 extend vertically intowaste mass 706; however, wells 701 may also extend horizontallythroughout waste mass 706, as shown in FIG. 7 b, such that circulatedfluid flows laterally into waste mass 706. Similarly, wells 701 may alsobe placed at an incline (not shown) into waste mass 706. For wells thatare installed horizontally or at an angle, placement of wells 701 wouldoccur in stages as waste mass 706 is landfilled onto barrier 705. Thisallows waste mass 706 to cover wells after installation. For wells thatextend vertically into waste mass 706, installation may occur duringwaste placement or even after landfilling of waste mass 706 is complete.

Each well of network 701 may be filled with a highly conductive granularbackfill and covered with an insulating seal as described in system 600.A barrier 705 is shown to sit upon native subgrade soils 708. Waste mass706 is landfilled onto barrier 705 and covered by a low permeabilitycover 707. The network of heat extraction pipes channeled through wells701 are jointly and fluidly coupled to an integrated surface pipingsystem 702. The surface piping 702, represented by dotted lines,provides a communal channel for transporting processed fluid (not shown)to heat exchanger 703, located above surface 708. It should beappreciated by one of ordinary skill that surface piping 702 or heatexchanger 703 are not limited to placement above ground surface 708 andmay be partially or fully located below ground surface 708. Circulationpump 710 is coupled to piping 702 to provide fluid flow throughout theclosed loop system 700. In one embodiment, pump 710 is interposedbetween the heat extraction wells 707 and heat exchanger 703; however,circulation pump 710 may also be placed along circulation piping routedinto wells 707 to provide fluid flow throughout the system 700.

A microprocessor computer 711 coupled to both the heat exchanger 703 andcirculation pump 710 may be used to monitor and control pumping ratesand thermal transfer rates in the system. The computer 711 can receiveand manipulate signals including, for example, temperature, position,flow-rate, and time related to the circulated fluid via a network ofsensors (not shown) integrated into piping 702, circulation pipingrouted into wells 707, and waste mass 706.

The processing fluid circulated through piping 702 and throughout wells701 is self-contained. Thermal energy transferred to heat exchanger 703may provide heat to nearby facility 704 through a second fluid (notshown) passing through surface or subsurface piping 709. As discussedabove, facility 704 may be, but is not limited to, the landfill officeoperating system 700, a maintenance garage, or a nearby industrial,commercial, or residential facility.

Heat extraction system 700 also provides the means for creating asymbiotic relationship between facility 704 and waste mass 706. Whileelevated heat may be transferred as an alternative energy source fromwaste mass 706 to facility 704, heat conversely may be transferred fromfacility 704 to waste mass 706. This technique has the advantage ofaccelerating gas and heat production in the landfill because wastedecomposition rates generally increase with increased temperatures. Asdiscussed with reference to FIG. 4 c, HC is linearly related to initialwaste placement temperatures. Elevated HC values occur where the initialwaste temperatures are also increased. Therefore, in order to elevatethe initial waste temperature at a landfill, system 700 may also be usedto provide additional heat to waste mass 706.

Facility 704 may provide thermal energy to heat exchanger 703 throughpiping 709. The heat transferred to the integrated surface piping 702can be conductively distributed throughout heat extraction wells 701 towaste mass 706. Effectively controlling the HC of waste mass reduces lagtime between waste placement and optimal gas extraction. The result issuch that waste mass could approach optimal heat and gas productionlevels rapidly after waste placement at varying temperatures of theinitial waste. An example is provided with reference to FIG. 8.

Turning to FIG. 8, a more generalized trend of heat content as afunction of waste age is shown. As discussed above with reference toFIG. 5 and equation (2), HC increases in the first stage of the landfilllife cycle t1. During period t1, gas production rates also begin toincrease (not shown) until the HC reaches an elevated peak valuecharacterizing a second stage of the landfill life cycle t2. Similarly,the heat generated and gas production levels (not shown) also peaksduring t2. Following this period of optimal performance of the landfill,HC decreases during a third stage t3 of the landfill life cycle until astable lower value of HC, which ultimately approaches ambientconditions, is reached in the fourth stage t4.

Preferably, the optimal performance of a landfill is described by themost efficient thermal conditions for heat and gas production levels.For example, an optimal temperature for growth of mesophilic bacteria isapproximately 35-40° C. The optimal temperature range for growth ofthermophilic bacteria is approximately 50-60° C. Similar to the optimummesophilic range, optimal conditions for landfill gas production—mostnotably, of methane—occurs between 34-41° C. These temperature rangesprovide targets for optimal performance of a landfill relative to gasproduction capacity. A system, such as system 700, that supports thermalheat exchange can obtain these conditions in waste mass 706 at anaccelerated rate. Once the landfill reaches a stable stage of heatproduction, the system may return to providing heat from waste mass 706to facility 704, thereby creating a symbiotic relationship benefittingboth waste mass 706 and facility 704. Preferably, the symbiotic processwould operate as follows.

In FIG. 8, during the early stage t1 of a landfill life cycle, both HCand gas production rates increase. In one embodiment of controlling thetemperature of waste mass 706, facility 704 can provide additional heatto heat exchanger 703 through piping 709 during t1. Heat is exchanged tointegrated surface piping 702 and can be circulated through network 701of heat exchange wells to provide additional heat to waste mass 706.This additional heat can accelerate heat generation (and thereforeincrease HC) and gas production rates similar to providing an electrical“jumpstart” to a battery of an internal combustion engine vehicle. Oncepeak performance of the landfill begins in stage t2, a symbioticrelationship may begin such that waste mass 706 can return heat tofacility 704 and provide a long-term source of thermal energy for use inindustrial heating. However, as discussed above, following the peakperformance of the landfill in stage t2, HC of the waste mass 706 maybegin to decrease during stage t3 until a stable lower level is reachedin t4. This decrease may benefit from additional heat exchange fromfacility 704. Providing heat to waste mass 706 once again during staget3 may reduce the rate at which heat generation and gas productionlevels are decreasing, thereby prolonging the optimal productive stageof the landfill prior to reaching stage t4. When the landfill eventuallyapproaches the stable levels of stage t4, system 700 can provide aconstant source of heat to facility 704 from waste mass 706. Forexample, waste mass 706, having a stable elevated temperature measuredat mid-depth, can heat a fluid circulating in the network of heatexchange wells 701 to a constant temperature above ambient temperatureconditions. Depending on seasonal climate fluctuations, this heatedfluid can proceed through integrated surface piping 702 towards heatexchanger 703 to be used for heating or cooling of facility 704. Theproduction of a constant source of heat creates a renewable energysource similar to a conventional ground heat source pump.

In an alternative embodiment of controlling temperature, during theearly stage t1 of a landfill life cycle, facility 704 can insteadprovide cooler temperatures to heat exchanger 703 through piping 709.This cooler temperature is exchanged to integrated surface piping 702and can be circulated through network 701 of heat exchange wells to cooltemperatures within waste mass 706. Unlike providing additional heat, asdescribed above, this cooling effect can delay heat generation (andtherefore postpone elevated HC) and gas production rates. This wouldprovide an opportunity to delay significant capital expenditure, forexample, associated with construction of a gas collection system duringthis time. Once peak performance of the landfill begins in stage t2, asymbiotic relationship may begin, similarly as discussed above, suchthat waste mass 706 can return heat to facility 704 and provide along-term source of thermal energy for use in industrial heating.Following the peak performance of the landfill in stage t2, HC of thewaste mass 706 may begin to decrease during stage t3 until a stablelower level is reached in t4. This decrease may benefit from additionalheat exchange from facility 704. Providing heat to waste mass 706 onceagain during stage t3 may reduce the rate at which heat generation andgas production levels are decreasing, thereby prolonging the optimalproductive stage of the landfill prior to reaching stage t4. When thelandfill eventually approaches the stable levels of stage t4, system 700can provide a constant source of heat to facility 704 from waste mass706. Depending on seasonal climate fluctuations, this heated fluid canproceed through integrated surface piping 702 towards heat exchanger 703to be used for heating or cooling of facility 704. The production of aconstant source of heat creates a renewable energy source similar to aconventional ground heat source pump.

Although the previous embodiments are based on the waste mass 706 havingdecomposition stages as shown in FIG. 8, the system would be applicablein other types of waste landfills. In addition to municipal solid wastelandfills, elevated temperatures also have been observed in other typesof landfills. For example, in a case study, Klein et al. (2001) reportedthat temperatures up to 87° C. were observed at a municipal solid wasteincineration bottom ash landfill. These elevated temperatures were dueto exothermic reactions occurring in the waste mass with the highesttemperatures occurring in the central zones of the waste mass.Additional information can be found in Klein, R., et al., for“Temperature development in a modern municipal solid waste incineration(MSWI) bottom ash landfill with regard to sustainable waste management”(Klein, R., Baumann, T., Kahapka, E., Niessner, R., Journal of HazardousMaterials, B83, p. 265-80 (2001)), which is hereby incorporated byreference in its entirety. Although these various waste types may notdisplay similar biochemical reactions as shown in FIG. 8, system 700 maystill be used to exchange heat and control temperature within thesevarious waste types.

In addition to the preceding benefits, managing the temperature of wastemass 706 can directly influence the geomechanical behavior of the wastemass. The engineering properties of soils vary as a function oftemperature. For example, see Mitchell, J. K. & Soga, K., Fundamentalsof Soil Behavior, John Wiley & Sons, Inc. Hoboken, N.J. (3rd ed. 2005),which is hereby incorporated by reference in its entirety. Theparticulate structure of geomaterials is affected by changes intemperature due to particle contact characteristics. Stiffness andstrength of particle contacts have been described using the rate processtheory, and temperature-dependent prediction models using this theoryhave been developed to predict soil settlement. Fox, P. J., “An Analysisof One-Dimensional Creep of Peat,” Ph.D. Thesis, University ofWisconsin, Department of Civil and Environmental Engineering, MadisonWis. (1992), which is hereby incorporated by reference in its entirety.Fluids within geomaterials—typically water—are also affected by changesin temperature. Viscosity of fluids change with temperature and excesspore water pressures are developed due to differential thermal expansionof liquid and solid phases of the composite materials. Campanella, R. G.& Mitchell, J. K., “Influence of Temperature Variations on SoilBehavior,” Journal of Soil Mechanics and Foundation Engineering, ASCE,Vol. 94, SM3, p. 709-734 (1968), which is hereby incorporated byreference in its entirety. Analogies between engineering behavior ofwastes (i.e., shear strength, compressibility, and hydraulicconductivity) and soils have been commonly reported. Therefore, similardependence of temperature on waste properties is expected astemperature-dependent tests on the engineering properties of wastes havebeen reported in, for example, Lamothe, D. & Edgers, L., “The Effects ofEnvironmental Parameters on the Laboratory Compression of Refuse,”Proceedings of the 17th International Madison Waste Conference,University of Wisconsin, Madison, Wis., p. 592-604 (1994), which ishereby incorporated by reference in its entirety. Accordingly, similarto the heat generating properties discussed above, manipulation of thethermal energy of waste mass 706 can also regulate the engineeringbehavior of the waste mass.

In the foregoing specification, the invention has been described withreference to specific embodiments thereof. It will, however, be evidentthat various modifications and changes may be made thereto withoutdeparting from the broader spirit and scope of the invention. Forexample, the reader is to understand that the specific ordering andcombination of process actions described herein is merely illustrative,and the invention may appropriately be performed using different oradditional process actions, or a different combination or ordering ofprocess actions. For example, this invention is particularly suited formunicipal solid waste landfills; however, the invention can be used foran ash landfill, chemical or industrial waste landfill, or any organicdegradation system. Additionally and obviously, features may be added orsubtracted as desired. Accordingly, the invention is not to berestricted except in light of the attached claims and their equivalents.

What is claimed is:
 1. A temperature control and heat exchange systemcomprising: a closed-loop fluid circulation pipe; at least one heattransfer well providing a thermal encasement for the closed-loop fluidcirculation pipe, the heat transfer well filled at intervals with ahighly conductive granular backfill; wherein the at least one heattransfer well is installed in a waste mass; a heat exchanger having aninlet and outlet for a first circulation fluid and an inlet and outletfor a second circulation fluid; a circulation pump operatively coupledto the closed-loop circulation pipe to provide fluid flow for the firstcirculation fluid; and wherein the heat exchanger is fluidly coupled tothe closed-loop fluid circulation pipe at the inlet and outlet for thefirst circulation fluid such that the first circulation fluid, whencirculated through the closed-loop fluid circulation pipe via thecirculation pump into the at least one heat transfer well distributed inthe waste mass, transfers thermal energy between the waste mass and thesecond circulation fluid through the heat exchanger.
 2. The system ofclaim 1, wherein the waste mass has a first, second, third, and fourthlife cycle stage of biochemical processes, the heat exchanger transfersa first level of thermal energy from the second circulation fluid to thefirst circulation fluid at the first life cycle stage of biochemicalprocesses, extracts a second level of thermal energy from the firstcirculation fluid to the second fluid at the second life cycle stage ofbiochemical processes, transfers a third level of thermal energy fromthe second circulation fluid to the first circulation fluid at a thirdlife cycle stage of biochemical processes, and extracts a constantfourth level of thermal energy from the first circulation fluid to thesecond fluid at the fourth life cycle stage of biochemical processes. 3.The system of claim 2, wherein the transfer of a first level of thermalenergy from the second circulation fluid to the first circulation fluidat the first life cycle stage of biochemical processes cools the wastemass.
 4. The system of claim 2, wherein the transfer of a first level ofthermal energy from the second circulation fluid to the firstcirculation fluid at the first life cycle stage of biochemical processesprovides additional heat to the waste mass.
 5. The system of claim 1,further comprising a microprocessor computer coupled to both the heatexchanger and the circulation pump, the computer having means to controlfluid flow and thermal energy transfer of the first circulation fluidvia control signals to the heat exchanger and circulation pump.
 6. Thesystem of claim 5, further comprising a network of sensors, with meansfor measuring at least one of temperature, position, time, andflow-rate, integrated into the closed-loop fluid circulation pipe andthe waste mass, the network of sensors electronically coupled to thecomputer to provide control signals to the computer.
 7. The system ofclaim 1, wherein the at least one heat transfer well is installed in thewaste mass either vertically to provide vertical fluid flow through thewaste mass, horizontally to provide lateral fluid flow through the wastemass, or at an incline to provide inclined fluid flow through the wastemass.
 8. The system of claim 1, further comprising athermostat-controlled trace heater to prevent freezing of the firstcirculation fluid.
 9. The system of claim 1, wherein the heat exchangeris a plate and frame heat exchanger.
 10. The system of claim 1, whereinthe highly conductive granular backfill is dense gravel, soil, orindustrial byproduct.
 11. The system of claim 1, wherein the closed-loopfluid circulation pipe is cross-linked polyethylene (PEX), high densitypolyethylene, or copper.
 12. The system of claim 1, wherein the firstcirculation fluid is water, propylene glycol, or a water-glycol mixture.13. The system of claim 1, wherein the at least one heat transfer wellis covered by an insulating seal at a ground surface.
 14. A method oftemperature control and heat exchange of a waste mass comprising:routing at least one heat transfer well in the waste mass; channeling aclosed-loop fluid circulation pipe into the at least one heat transferwell, the at least one heat transfer well filled at intervals with ahighly conductive granular backfill for providing a thermal encasing forsaid closed-loop fluid circulation pipe; circulating a first circulationfluid through the closed-loop fluid circulation pipe via a circulationpump operatively coupled to the closed-loop circulation pipe; andexchanging heat between the first circulation fluid and a secondcirculation fluid via a heat exchanger having an inlet and outlet forthe first circulation fluid and an inlet and outlet for the secondcirculation fluid and is fluidly coupled to the closed-loop circulationpipe at the inlet and outlet for the first circulation fluid.
 15. Themethod of claim 14, wherein the heat exchanger and the circulation pumpare further coupled to a microprocessor computer providing means tocontrol fluid flow and thermal energy transfer of the first circulationfluid via control signals to the heat exchanger and circulation pump.16. The method of claim 14, wherein exchanging heat between the firstcirculation fluid and a second circulation fluid controls at least oneof shear strength, compressibility, and hydraulic conductivity of thewaste mass.
 17. The method of claim 14, wherein the first circulationfluid is water, propylene glycol, or a water-glycol mixture.
 18. Themethod of claim 14, comprising monitoring at least one of temperature,position, time, and flow-rate of the first circulation fluid via anetwork of sensors integrated into the closed-loop fluid circulationpipe and the waste mass, the network of sensors electronically coupledto the computer to provide control signals to the computer.